Communication system comprising an optical fiber assembly, a modulated light signal receiver and a telescope

ABSTRACT

A system includes an optical fiber assembly, a receiver and a telescope, the receiver being positioned at a receiving end of the optical fiber assembly, the telescope being positioned at a collecting end, the receiver being arranged to receive uplink modulated light signals collected by the telescope and travelling through the optical fiber assembly, the telescope comprising an optical concentrator having an inlet face and an outlet face with a surface area smaller than that of the inlet face, the telescope further including a gradient-index lens dispose d coaxially with respect to the optical concentrator so that an inlet face of the gradient-index lens extends opposite the outlet face of the optical concentrator, the collecting end of the optical fiber assembly opening out opposite an outlet face of the gradient-index lens.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the U.S. National Stage of PCT/EP2020/058217, filedMar. 24, 2020, which in turn claims priority to French patentapplication number 1903381 filed Mar. 29, 2019. The content of theseapplications are incorporated herein by reference in their entireties.

The invention concerns the field of communication systems comprising anoptical fiber assembly and a receiver of modulated light signals.

BACKGROUND OF THE INVENTION

Communication systems are known that include a light-transmitting diodelamp (here called LED lamp) and implement a technology called “VLC” (forVisible Light Communication). Such a communication system allows both toilluminate the environment of the LED lamp, and to transmit and receivemodulated light signals to allow wireless communication between thecommunication system and an electronic device located near the LED lamp.

In this type of communication system, electrical wires are required tocarry power currents to the LED lamp to drive the components with whichthe LED lamp is equipped. These components include a visible lighttransmitter (including one or more LED(s)), a modulated light signaltransmitter (including one or more LED(s)), a modulated light signalreceiver (including, for example, one or more photodiode(s)).

But in some environments, these electrical wires are very problematic.

It is known, for example, that some aircraft manufacturers are seekingto install such communication systems in aircraft cabins, so as toilluminate passengers and create communication networks using VLCtechnology and including passengers' electronic devices.

-   -   These communication networks allow passengers not only to access        various multimedia data in a simple and convenient way, but        also, possibly, to access the Internet. VLC technology is        particularly interesting in the aircraft cabin environment        because, unlike radio communication technologies, VLC technology        does not generate electromagnetic interference and does not        encounter frequency spectrum availability problems.

However, any electrical equipment installed in an aircraft must complywith particularly stringent standards regarding transmissions andsusceptibility to radio frequencies.

But electrical wires tend to transmit radio frequencies, making theelectrical equipments they connect susceptible to radio frequencies. Thenumber and length of electrical wires required to light all passengersand give them access to VLC technology make it very complex to integratea communication system using VLC technology into the cabin.

SUBJECT OF THE INVENTION

The invention relates to a communication system using VLC technology,wherein the length of electrical wires is reduced and the reception ofmodulated light signals is optimized.

SUMMARY OF THE INVENTION

In order to achieve this goal, a communication system is proposedcomprising an optical fiber assembly, a modulated light signal receiverand a telescope, the modulated light signal receiver being positioned ata receiving end of the optical fiber assembly, the telescope beingpositioned at a collecting end of the optical fiber assembly, themodulated light signal receiver being arranged to receive uplinkmodulated light signals collected by the telescope and travelling in theoptical fiber assembly, the telescope comprising an optical concentratorhaving an inlet face and an outlet face with a surface area smaller thanthat of the inlet face, the telescope further comprising agradient-index lens arranged with respect to the optical concentrator sothat an inlet face of the gradient-index lens extends opposite theoutlet face of the optical concentrator, the collecting end of theoptical fiber assembly opening out opposite an outlet face of thegradient-index lens.

In the communication system according to the invention, the receiver ofmodulated light signals is separated by an optical fiber assembly fromthe telescope that collects the uplink modulated light signals.

This optical fiber assembly can have a relatively long length andreplaces electrical wires with equivalent lengths.

The telescope allows to collect very efficiently incident light rays,and thus to improve the reception of uplink modulated light signalstransmitted by an transmission device located near the telescope.

The invention will be better understood in light of the followingdescription of particular non-limiting embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference will be made to the attached drawings, among which:

FIG. 1 shows a communication system according to a first embodiment ofthe invention;

FIG. 2 shows the communication system according to the first embodimentof the invention;

FIG. 3 is a schematic and functional view similar to that of FIG. 2 ,showing a first dichroic filter and a second dichroic filter;

FIG. 4 shows an optical fiber assembly of the communication systemaccording to the first embodiment of the invention;

FIG. 5 is a graph showing a transmittance curve and a reflectance curveof the first dichroic filter;

FIG. 6 is a graph showing a transmittance curve and a reflectance curveof the second dichroic filter;

FIG. 7 shows a telescope of the communication system according to thefirst embodiment of the invention;

FIG. 8 shows a telescope of a communication system according to a secondembodiment of the invention;

FIG. 9 shows a telescope of a communication system according to a thirdembodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

With reference to FIGS. 1 to 4 , the invention is here implemented in anaircraft cabin. The aircraft cabin comprises a plurality of seats 1 eachintended to accommodate a passenger 2. Each passenger 2 thus has apersonal space. Each passenger 2 is possibly equipped with an electronicdevice 3, which is for example a laptop, a smartphone, a tablet, aconnected watch, etc.

The communication system according to a first embodiment of theinvention is intended to illuminate each passenger 2, and to implement aVLC technology to allow each passenger 2 to communicate, through theirelectronic device 3, with a computer terminal 4 of the aircraft. Eachpassenger 2 can thus access various multimedia data stored in thecomputer terminal 4, and can also access the Internet via the computerterminal 4.

To communicate with the aircraft's computer terminal 4, the passenger'selectronic device 3 must be equipped with a VLC transmitting andreceiving device. The VLC transmitting and receiving device is eitherdirectly integrated into the electronic device 3 or is connected to theelectronic device 3. The VLC transmitting and receiving device is thus,for example, a dangle connected to the electronic device 3, possibly viaa USB port of the electronic device 3.

The lighting and communication system here comprises a centralizedlighting module 6, a centralized communication module 7, and a pluralityof lighting devices 8, each lighting device 8 being associated with apersonal space.

The centralized lighting module 6 includes visible light transmitters 9,each visible light transmitter 9 being associated with a personal space,and control components 10. Each visible light transmitter 9 comprises afirst light transmitting diode (LED) 11.

When it is necessary to illuminate a personal space of a passenger 2,the control components 10 generate a supply current to the first LED 11of the visible light transmitter 9 associated with the personal space.The first LED 11 generates light from the supply current, the spectrumof which is contained in the visible range.

The centralized communication module 7 comprises a modem 13, and aplurality of modulated light signal transmitters 15 and modulated lightsignal receivers 16, a pair of one modulated light signal transmitter 15and one modulated light signal receiver 16 being associated with apersonal space of a passenger 2.

The modem 13 is electrically connected to the modulated light signaltransmitters 15 and the modulated light signal receivers 16.

The modem 13 is also electrically connected to the aircraft's computerterminal 4, for example via an Ethernet cable.

Each modulated light transmitter 15 includes a second LED 20. The secondLEDs 20 produce light with a spectrum in the infrared range.

Each modulated light signal receiver 16 comprises a photodiode 21. Thephotodiode 21 is here an avalanche photodiode, sensitive to light whosespectrum is contained in the infrared range.

When a communication is established between the computer terminal 4 anda personal space VLC transmitting and receiving device, the modem 13acquires downlink data from the computer terminal 4, The modem 13produces a supply current to the second LED 20 of the correspondingmodulated light signal transmitter 15. The power supply current switchesthe second LED 20, so as to switch a light power produced by the secondLED 20 to generate downlink modulated light signals to the VLCtransmitting and receiving device of the personal space, said downlinkmodulated light signals containing the downlink data.

Similarly, the photodiode 21 of the corresponding modulated light signalreceiver 16 receives uplink modulated light signals from the VLCtransmitting and receiving device of the electronic device 3 of thepassenger 2 of the personal space. The photodiode 21 converts the uplinkmodulated light signals into electrical signals containing uplink data.

The modem 13 acquires the electrical signals containing the uplink data.

The modern 13 thus receives all the uplink and downlink data exchangedbetween the computer terminal 4 and the electronic devices 3 of thepassengers 2, and formats these data to make them compatible, on the onehand, with the second LEDs 20, and on the other hand, with the receiversof computer terminal 4.

We note here that the centralized lighting module 6 and the centralizedcommunication module 7 can be arranged on one or more electrical boards,distinct or not, positioned in the same box or in several boxes. Theboxes can be close together or, on the contrary, far apart, and belocated in the cabin or in any other place inside the aircraft.

Each lighting device 8 comprises a light diffuser 25 and an opticalfiber assembly 26.

The light diffuser 25 extends over the personal space of a passenger 2and provides both illumination of the personal space and an exchange ofmodulated uplink and downlink light signals with the VLC transmittingand receiving device of the passenger 2's electronic device 3. The lightdiffuser 25 thus acts both as a lamp lens, and as an uplink lightinjector into the optical fiber assembly 26.

The optical fiber assembly 26 includes a first optical fiber portion 31,a second optical fiber portion 32, a third optical fiber portion 33, afourth optical fiber portion 34 and a fifth optical fiber portion 35.

A visible light transmitter 9 is positioned at a first end of the firstoptical fiber portion 31. More specifically, the first end of the firstoptical fiber portion 31 and a first LED 11 extend opposite each otherand are optically coupled via a lens. The first end of the first opticalfiber portion 31 will also be referred to as the “lighting end”.

A modulated light signal transmitter 15 is positioned at a first end ofthe second optical fiber portion 32. More specifically, the first end ofthe second optical fiber portion 32 and a second LED 20 extend oppositeeach other and are optically coupled via a lens. The first end of thesecond optical fiber portion 32 will also be referred to as the“transmitting end”.

A second end of the first optical fiber portion 31 and a second end ofthe second optical fiber portion 32 are coupled and connected, at afirst connection area 40, to a first end of the third optical fiberportion 33. The coupling is performed according to a conventional methodof optical fiber coupling.

The second end of the first portion of optical fiber 31 and the secondend of the second portion of optical fiber 32 are therefore joined inthe first connection area 40 to open at the first end of the thirdportion of optical fiber 33.

The second end of the first optical fiber portion 31 the second end ofthe second optical fiber portion 32 and the first end of the thirdoptical fiber portion 33 thus form a first coupler 2×1.

A first dichroic filter 41 is integrated into the first connection area40. The first dichroic filter 41 is made of a large amount of thinlayers. The first dichroic filter 41 extends into a section of thesecond end of the second optical fiber portion 32, slightly upstream ofthe contact area between the second end of the first optical fiberportion 31 and the second end of the second optical fiber portion 32. By“upstream” is meant on the side of a LED or photodiode and not on theside of the light diffuser 25.

The transmittance curve 49 and reflectance curve 50 of the firstdichroic filter 41 are shown in FIG. 5 .

It can be seen that the first dichroic filter 41 allows light signalswith a wavelength greater than or equal to 850 nm to pass and reflectsthose with a wavelength less than or equal to 700 nm.

The role of the first dichroic filter 41 is to avoid light returns inthe second portion of optical fiber 32, and therefore losses on thefirst portion of optical fiber 31.

The first connection area 40 is integrated into a first housing 44 of afirst multiplexer.

A modulated light signal receiver 16 is positioned at a first end of thefourth optical fiber portion 34. More specifically, the first end of thefourth optical fiber portion 34 and a photodiode 21 extend opposite eachother and are optically coupled via a lens. The first end of the fourthoptical fiber portion 34 will also be referred to as the “receivingend”.

A second end of the third optical fiber portion 33 and a second end ofthe fourth optical fiber portion 34 are coupled and connected at asecond connection area 51 to a first end of the fifth optical fiberportion 35. The coupling is again performed in a conventional opticalfiber coupling method.

The second end of the third optical fiber portion 33 and the second endof the fourth optical fiber portion 34 meet in the second connectionarea 51 to open at the first end of the fifth optical fiber portion 35.

The second end of the third optical fiber portion 33, the second end ofthe fourth optical fiber portion 34 and the first end of the fifthoptical fiber portion 35 thus form a second coupler 2×1.

A second dichroic filter 52 is integrated into the second connectionarea 51. The second dichroic filter 52 is made of a large amount of thinlayers. The second dichroic filter 52 extends into a section of thesecond end of the fourth optical fiber portion 34, slightly upstream ofthe contact area between the second end of the third optical fiberportion 33 and the second end of the fourth optical fiber portion 34.

The transmittance curve 54 and the reflectance curve 55 of the seconddichroic filter 52 are shown in FIG. 6 .

It can be seen that the second dichroic filter 52 allows light signalswith a wavelength greater than or equal to 940 nm to pass and reflectsthose with a wavelength less than or equal to 850 nm.

The role of the second dichroic filter 52 is to separate the differentwavelengths.

The second connection area 51 is integrated in a second housing 56 of asecond multiplexer.

It is noted that the diameter of each fiber portion doesn't matter, andcould for example be between 0.2 mm and 3 mm. The fiber portions can bemade of glass or plastic or any other material.

It is noted here that the first optical fiber portion 31, intended forlighting, is a multimode fiber, that the second optical fiber portion32, intended for data transmission, can also be a multimode fiber, andthat the third optical fiber portion 33 is therefore also a multimodefiber. This is also true for the fourth optical fiber portion 34 and thefifth optical fiber portion 35.

The communication and lighting system works as follows for each personalspace.

A first LED 11 produces visible light 60. The visible light 60propagates through the first fiber portion 31, is reflected by the firstdichroic filter 41, which prevents the visible light 60 from propagatingthrough the second optical fiber portion 32.

The second dichroic filter 52 allows visible light 60 to pass downward,which propagates through the fifth optical fiber portion 35. The secondend of the fifth optical fiber portion 35 opens to the outside of theoptical fiber assembly 26, in this case into the light diffuser 25.Visible light is transmitted through the second end of the fifth opticalfiber portion 35 and through the light diffuser 25 to illuminate thepersonal space of the passenger 2.

A downlink communication is furthermore established between a modulatedlight signal transmitter 15 and the VLC transmitting and receivingdevice of the electronic device 3 of the passenger 2. Downlink modulatedlight signals 61, containing downlink data from the computer terminal 4,are transmitted from a second LED 20. The downlink modulated lightsignals 61 have a wavelength equal to 850 nm. The downlink modulatedlight signals 61 propagate through the second optical fiber portion 32,and are not blocked but are transmitted through the first dichroicfilter 41 to propagate through the third optical fiber portion 33 (seetransmittance curve 49 and reflectance curve 50).

The downlink modulated light signals 61 then propagate into the thirdoptical fiber portion 33. The second dichroic filter 52 does not passthe downlink modulated light signals 61 into the fourth optical fiberportion 34 (see transmittance curve 54 and reflectance curve 55). Thedownlink modulated light signals 61 therefore propagate through thefifth optical fiber portion 35, are transmitted via the second end ofthe fifth fiber portion 35 and via the light diffuser 25, and aretransmitted to the VLC transmit/receive device of the electronic device3 of the passenger 2.

The electronic device 3 then acquires the downlink data.

An uplink communication is also established between the VLC transmittingand receiving device of the passenger's electronic device 3 and amodulated light signal receiver 16. Uplink modulated light signals 62,containing uplink data to the computer terminal 4, are transmitted bythe VLC transmitting and receiving device. The uplink modulated lightsignals 62 have a wavelength equal to 950 nm. The uplink modulated lightsignals 62 are picked up by the light diffuser 25. The uplink modulatedlight signals 62 propagate into the fifth optical fiber portion 35 viathe second end of the fifth optical fiber portion 35. The seconddichroic filter 52 passes the uplink modulated light signals 62 into thefourth optical fiber portion 34. The uplink modulated light signals 62thus propagate in transmission through the fourth optical fiber portion34 and are picked up by the photodiode 21 of the modulated light signalreceiver 16.

The modem 13 of the centralized communication module 7 then acquires theuplink data and transmits them to the computer terminal 4.

With reference to FIG. 7 , a telescope 70 is positioned at a second endof the fifth optical fiber portion 35. The second end of the fifthoptical fiber portion 35 will also be referred to as the “collectingend”.

By “telescope” is meant here an optical instrument that forms, from anobject located on one side of the telescope and at an infinite objectdistance from it, an image of the object located on the other side ofthe telescope and at an infinite image distance from it.

By “infinite object distance” and “infinite image distance” are meanthere very large distances with respect to the diameter of the surface ofthe corresponding telescope face, i.e. typically more than 10 or 100times a larger telescope diameter.

First, the telescope 70 includes an optical concentrator 71. Theconcentrator 71 is here a compound elliptical concentrator.

The concentrator 71 has an axis of revolution Z. The concentrator 71includes a main portion 72 and a cylindrical portion 73.

The outer shape of the main portion 72 is defined by a lateral surface78 that extends between an inlet face 74 and an outlet end 75.

The inlet end 74 of the concentrator 71 is also an inlet end of thetelescope 70. The outlet end 75 is shaped like a disk. The inlet face 74and the outlet end 75 extend perpendicular to the Z axis.

The area of the inlet face 74 is greater than the area of the outlet end75.

The lateral surface 78 is defined, in a sectional plane passing throughthe Z axis, by a first elliptical arc 76 and by a second elliptical arc77.

We note here that the concentrator 71 can be designed from any curvedsurface of the “unruled” type (i.e., not containing a straight line).This includes all so-called free surfaces, i.e. surfaces described by acurve at the vertex, by a conical constant, by non-zero deformationcoefficients, and finally by a rotation angle. This angle of rotation isnone other than the angle of rotation of the surface defined as thestarting base surface of the optical design of the concentrator 71. Thebase surface is, for example, an ellipse of revolution, or any unruledsurface. The angle of rotation thus characterizes any compoundconcentrator.

It should be noted that the lateral surface 78 of the main portion 72 ofthe concentrator 71 of the lighting system may have one or more lateralfacets of the prismatic type.

The outlet end 75 opens into the cylindrical portion 73 which has across-sectional area equal to the area of the outlet end 75. An outletface 80 of cylindrical portion 73 forms an outlet face 80 ofconcentrator 71. The area of the outlet face 80 of the concentrator 71is smaller than the area of the inlet face 74 of the concentrator 71 andthe telescope 70.

The inlet face 74 is now described.

It would be possible to provide that the inlet face 74 has a surfacedefined by a Cartesian oval.

In the cylindrical reference frame (r, Z(r)), this Cartesian oval wouldhave the equation:

${{z_{a}(r)} = {\frac{c_{a}r^{2}}{1 + \sqrt{1 - {\left( {1 + K_{a}} \right)\left( {c_{a}r} \right)^{2}}}} + {\sum\limits_{j = 2}^{7}\;{A_{2\; j}r^{2\; j}}}}},$where C_(a) is the curvature at the vertex of the Cartesian oval (alsocalled vertex curvature), K_(a) is a conic constant, and A_(2j) aredeformation coefficients. It is assumed that the inlet face 74 has arelative refractive index n and accepts light from a light sourcealigned on the optical axis at an object focal length t_(a). The inletface 74 then produces a diffraction-limited image (because the inletface 74 does not introduce spherical aberration) at an image focallength t′_(a).

The parameters of the Cartesian oval equation can be calculated usingthe recurrent variables:m=n−1,p=n+1,U=nt _(a) −t′ _(a), and V=2mt _(a) t′ _(a).

The curvature at the vertex C_(a) is such that:C _(a)=2U/V.

An example of a set of deformation coefficients A_(2j) is provided inAppendix 1, at the end of this description.

An example of a set of characteristic polynomials P_(2j), used in thedefinition of the deformation coefficients A_(2j), is provided inAppendix 2 at the end of this description.

Here, however, as can be seen in FIG. 7 , the inlet face 74 has aFresnel surface, and thus acts as a Fresnel lens.

The Fresnel surface faces outward and has a plurality of areas 81 in theform of concentric annular sections centered on the Z axis. Theconcentric annular sections are defined by steps that extend outwardfrom the inlet face 74.

The use of the Fresnel surface reduces the volume of the inlet face 74of the telescope 70 (and thus the volume and mass of the telescope 70).

The Fresnel surface is defined by a piecewise function, each piececorresponding to an area 81 having the shape of a concentric annularsection centered on the Z axis.

Each piece has a surface defined by a Cartesian oval.

The Fresnel surface used here does not introduce any sphericalaberration, which allows the incident light rays to be perfectlyconcentrated at the image focus of the Fresnel lens constituted by theinlet face 74. The image focus F is located at the center of the outletend 75 of the main portion 72 of the concentrator 71.

To define the Fresnel surface, a definition method is implementedcomprising the following steps:

Step 1:

We define a height h for each piece (h can vary or be constant);

Step 2:

We define the diameter d of the surface of the piece;

Step 3:

We initialize a piece counter=1 (each piece is associated to a distinctvalue of i);

Step 4:

As long as the abscissa r_(s)(i)≤d/2, the definition method progresses;

Step 5:

We define the piece i using the equation:

${z_{a}(r)} = {{\left( {1 - i} \right)h} + \frac{c_{a}r^{2}}{1 + \sqrt{1 - {\left( {1 + K_{a}} \right)\left( {c_{a}r} \right)^{2}}}} + {\sum\limits_{j = 2}^{7}\;{A_{2\; j}r^{2\; j}}}}$

The parameters are identical to those used earlier for the Cartesianoval, except that the object focal length to and the image focal lengtht′_(a) are compensated:t _(a) =t _(a)−(i−1)h,t′ _(a) =t′ _(a)+(i−1)h.

We thus obtain z_(a) which depends on the following parameters:z _(a) [n,t _(a)−(i−1)h,t′ _(a)+(i−1)h,K _(a) , r _(c)].Step 6:

The positive abscissa r_(c)[i] of the string, which corresponds to aheight h in the interval {0,d/2}, is calculated numerically using thefunction:FindRoot[(1−i)h+z _(a) [n,t _(a)−(i−1)h,t′ _(a)+(i−1)h,K _(a) , r _(c)]=h;Step 7:

We define, for the following piece i+1:t _(a) =t _(a) −ih,t′ _(a) =t′ _(a) +ih;Step 8:

We define the next piece i using the previous equations whileconsidering the compensated offset (i.e. translation), as well as thecompensated distances at the maximum diameter.z _(a) [i+1]={−ih+z _(a) [n,t _(a) −ih,t′ _(a) +ih,K _(a) , r],(r>−d/2 and r=−r _(c) [i]) or (r<d/2 and r>=r _(c) [i])};Step 9:

We then redefine the domain for the previous sector.(r>−rc[i] and r=r _(c)[1−i]) or (r<r _(c) [i] and r>=r _(c) [i−1]);Step 10:

The piece is added to the function:Rule=Append [fresnel, piece_z_(a)[i]];Step 11:

The piece counter is then incremented: i=i+1;

Step 12:

The loop is closed, and the definition method returns to step 4,

Step 13:

The last piece is added:Rule=Append [fresnel, piece_z_(a)[i]].Step 14:

We then perform the correction of the riser of the Fresnel lens. Forthis, we follow the direction of the emerging rays using ray tracing.

An example of a set of parameters and implementation of an algorithmassociated with the definition method is provided in Appendix 3, at theend of this description.

The concentrator 71 and the Fresnel lens formed by the Fresnel surfaceof the inlet face 74, thus form a monolithic assembly.

The telescope 70 further includes a gradient-index lens 83. Thegradient-index lens 83 is arranged coaxially with respect to theconcentrator 71 along the Z axis. The gradient-index lens 83 is made ofa material whose refractive index changes in a radial, axial direction,or in aspherical way.

The gradient-index lens 83 has a cylindrical shape equal incross-section to the cylindrical portion 73. The gradient-index lens 83extends from the outlet face 80 of the concentrator 71.

The gradient-index lens 83 has an inlet face 86 that extends oppositethe outlet face 80 of the concentrator 71.

The inlet face 86 of the gradient-index lens 83 is positioned againstthe outlet face 80 of the concentrator 71 and is bonded to the outletface 80. The adhesive used has a refractive index similar to thematerial used to make the concentrator 71 and the gradient-index lens83.

The telescope 70, including the gradient-index lens 83 and theconcentrator 71, thus forms a monolithic assembly.

The second end of the fifth optical fiber portion 35 here has across-section equal to that of the gradient-index lens 83. The secondend of the fifth optical fiber portion 35 opens facing the outlet face87 of the telescope 70. The second end of the fifth optical fiberportion 35 is coupled to the outlet face 87 of the telescope 70, whichis also an outlet face 87 of the gradient-index lens 83, The couplinghere uses an APC connector, but another type of connector could be used.The coupling could be accomplished in a different manner, such as bybonding.

A ferrule 84 extends around the cylindrical portion 73, thegradient-index lens 83, and a short length of the second end of thefifth optical fiber portion 35. The ferrule 84 consolidates theattachment of the concentrator 71 the gradient-index lens 83, and thesecond end of the fifth optical fiber portion 35 to each other.

The operation of the telescope 70 is now described.

As can be seen in FIG. 1 , the telescope 70 extends vertically into thelight diffuser 25, so that the inlet face 74 of the telescope 70 opensto the exterior of the lighting and communication system, facing thepersonal space of the passenger 2.

The telescope 70 firstly has the advantages of the concentrator 71 andthe Fresnel lens formed by the Fresnel surface of the inlet face 74. Thetelescope 70 thus allows the collection of incident light rays with alarge acceptance angle. The acceptance angle here is equal to 34°.Incident light rays entering the concentrator 71 through the inlet face74 are concentrated by reflection at the inner lateral surface of themain portion 72 of the compound elliptical concentrator 71.

If only a conventional optical concentrator were used, the incidentlight rays would be concentrated on an edge of the outlet end 75 of themain portion 72. With the use of the concentrator 71 described herein,the incident light rays are concentrated on the center of the outlet end75, and then redistributed into the gradient-index lens 83 andthroughout the cross-section of the second end of the fifth opticalfiber portion 35.

The use of the telescope 70 thus optimizes the collection andconcentration, in the second end of the fifth optical fiber portion 35,of incident light rays coming from outside the light diffuser 25 andthus, in particular, from the personal space of the passenger 2. Thereception, by the lighting and communication system, of the uplinkmodulated light signals transmitted by the VLC transmission andreception device of the electronic device 3 of the passenger 2 andintended to be received by a modulated light signal receiver 16 is thusgreatly improved.

Visible light and downlink modulated light signals propagate from thesecond end of the fifth optical fiber portion 35 into the personal spaceof the passenger 2 via the telescope 70.

With reference to FIG. 8 , a telescope 90 of a communication systemaccording to a second embodiment of the invention includes an opticalconcentrator 91 and a gradient-index lens 92 too.

An inlet face of the gradient-index lens 92 is bonded to an outlet faceof the optical concentrator 91. The optical concentrator 91 and thegradient-index lens 92 thus form a monolithic telescope 90. It is notedthat the outlet face 93 of the gradient-index lens 92, which is also theoutlet face of the telescope 90, is flat. This facilitates the couplingof the second end of the fifth optical fiber portion 35 to the outletface 93.

The inlet face 94 of the optical concentrator 91 of the telescope 90 hasa convex surface defined by the equation:

$Z_{a} = {\frac{n}{n + 1}\left( {{- f_{a}} + {\sqrt{\left. {f_{a}^{2} - {\frac{n + 1}{n - 1}r^{2}}} \right)}.}} \right.}$The outlet face 93 is defined by the equation:Z _(b) =t=f _(a) +l, with f _(a) ,l>0.

In these equations, fa is the image focal length of the lens formed bythe convex surface of the inlet face 94, and n is the index of thematerial from which the optical concentrator 91 is made.

With reference to FIG. 9 , a telescope 100 of a communication systemaccording to a third embodiment of the invention is similar to that ofthe second embodiment, except that the lateral surface is defined, in across-sectional plane passing through the Z-axis, by a first ellipticalarc 106 and by a second elliptical arc 107.

The internal lateral surface of the telescope allows to increase theacceptance angle. The internal lateral surface reflects completely theincident light rays.

The entrance face 104 of the optical concentrator 101 of the telescope100 again has a convex surface defined by the equation:

$Z_{a} = {\frac{n}{n + 1}\left( {{- f_{a}} + {\sqrt{\left. {f_{a}^{2} - {\frac{n + 1}{n - 1}r^{2}}} \right)}.}} \right.}$

The invention is not limited to the particular embodiments justdescribed, but, on the contrary, covers any variant falling within thescope of the invention as defined by the claims.

Each lighting device, comprising a light diffuser and an optical fiberassembly, has been associated here with a modulated light signaltransmitter and a modulated light signal receiver. It is also possibleto have several transmitters and/or several receivers associated withthe same lighting device, each transmitter and each receiver beingpositioned at one end of a portion of optical fiber of the optical fiberassembly. It is also possible to have a single transmitter and/orreceiver connected to a plurality of lighting devices. The communicationmodule may include a single or multiple communication channels. Any typeof network can thus be implemented using any type of link andmultiplexing configuration, and in particular MIMO (for Multiple InputMultiple Output) or MISO (for Multiple Input Single Output) type links.

It would have been possible to replace at least one of the two dichroicfilters with a thin reflective layer made of a reflective materialdeposited in the corresponding connection area.

To build the telescope, any kind of optical concentrator can be used,and in particular a compound parabolic concentrator (or CPC), a coupledconcentrator comprising a first concentrator integrated in a secondconcentrator, a solid or hollow concentrator, a Lens-walled typeconcentrator, etc.

The telescope could be a compound focal telescope, a compound afocaltelescope, a monolithic focal telescope, a monolithic afocal telescope,etc.

An example of a monolithic afocal telescope is a telescope comprising abi-elliptical and biconvex lens. The focal plane of such a telescope islocated inside the monolithic block forming the telescope.

It has been indicated that the inlet face of the gradient-index lensextends opposite the outlet face of the optical concentrator. It ismeant here either that the gradient-index lens is positioned against theoutlet face of the optical concentrator, as is the case in thisdescription, or that the gradient-index lens and the outlet face of theoptical concentrator are separated only by an at least partiallytransparent element (another lens, some kind of attachment element,etc.). This is also the case between the receiving end of the opticalfiber assembly and the outlet face of the gradient-index lens.

It has also been indicated that the inlet face of the telescope can havea surface defined by a Cartesian oval or a Fresnel surface. It would bepossible to replace this inlet face with a corresponding lens, i.e. alens with a surface defined by a Cartesian oval or a Fresnel lens, andto position this lens against the inlet face of the opticalconcentrator.

Annex 1

The deformation coefficients A_(2j) are for example the following:

${{A_{4}\left( K_{a} \right)} = \frac{{m\; P_{4}} - {U^{3}\left( {1 + K_{a}} \right)}}{V^{3}}},{{A_{6}\left( K_{a} \right)} = {2\left( \frac{{m^{2}P_{6}} - {U^{5}\left( {1 + K_{a}} \right)}^{2}}{V^{5}} \right)}},{{A_{8}\left( K_{a} \right)} = {5\left( \frac{{m^{3}P_{8}} - {U^{7}\left( {1 + K_{a}} \right)}^{3}}{V^{7}} \right)}},{{A_{10}\left( K_{a} \right)} = {2\left( \frac{{m^{4}P_{10}} - {7{U^{9}\left( {1 + K_{a}} \right)}^{4}}}{V^{9}} \right)}},{{A_{12}\left( K_{a} \right)} = {14\left( \frac{{m^{5}P_{12}} - {3{U^{11}\left( {1 + K_{a}} \right)}^{5}}}{V^{11}} \right)}},{{A_{14}\left( K_{a} \right)} = {12\left( \frac{{m^{6}P_{14}} - {11{U^{13}\left( {1 + K_{a}} \right)}^{6}}}{V^{13}} \right)}},$

Annex 2

The characteristic polynomials P_(2j) are for example the following:

P₄ = [n²t_(a)³ + t_(a)^(′3) + n(t_(a) + t_(a)^(′))(t_(a)² − 3 t_(a)t_(a)^(′) + t_(a)^(′2))], P₆ = [n p²t_(a)⁵ − 3n p t_(a)⁴ t_(a)^(′) − n(3 n − 1)t_(a)³ t_(a)^(′2) − n(n − 3)t_(a)² t_(a)³ + 3 np t_(a)t_(a)^(′4) − p²t_(a)^(′5)], P₈ = [n p³t_(a)⁷ − 4n p²t_(a)⁶ t_(a)^(′) − 4 n m p t_(a)⁵ t_(a)^(′2) − 2 n{n(n − 4) − 1}t_(a)⁴ t_(a)^(′3) + 2 n{n(n + 4) − 1}t_(a)³ t_(a)^(′4) + 4 n m p t_(a)²t_(a)^(′5) − 4 np²t_(a)t_(a)^(′6) + p³t_(a)^(′7)], P₁₀ = [7 np⁴t_(a)⁹ − 35 n p³t_(a)⁸ t_(a)^(′) − 5 n(7 n − 11)p²t_(a)⁷ t_(a)^(′2) − 10 n(2n² − 11 × n + 1)p t_(a)⁶ t_(a)^(′3) + 2 n(5 n³ + 63 n² − 15 n − 17)t_(a)⁵ t_(a)^(′4) + 2 n(17 × n³ + 15 n² − 63 n − 5)t_(a)⁴ t_(a)^(′5) + 10 n(n² − 11n + 2) p t_(a)³ t_(a)^(′5) − 5 n(11n − 7)p²t_(a)²t_(a)^(′7) + 35 n p ³t_(a) t_(a)^(′8) − 7 p⁴t_(a)^(′9)], P₁₂ = [3 np⁵t_(a)¹¹ − 18n p⁴t_(a)¹⁰ t_(a)^(′) − 2 n(9 n − 19)p³t_(a)⁹ t_(a)^(′2) − n(11n² − 76 n + 25)p²t_(a)⁸ t_(a)^(′3) + 3 n m p(n² + 30 n + 5)t_(a)⁷t_(a)^(′4) + 4 n(4 n⁴ + 11 n³ − 35 n² − 15 n + 3)t_(a)⁶t_(a)^(′5) + 4 n(3 n⁴ − 15 n³ − 35 n² + 11n + 4) × t_(a)⁵t_(a)^(′6) − 3 n m p(5n² + 30 n + 1)t_(a)⁴t_(a)^(′7) − n(25 n² − 76 n + 11) × p²t_(a)³t_(a)^(′8) + 2 n(19 n − 9)p³t_(a)² t_(a)^(′9) − 18n p⁴t_(a)t_(a)^(′10) + 3 p⁵t_(a)^(′11)], P₁₄ = [11 np⁶t_(a)¹³ − 77n p⁵t_(a)¹² t_(a)^(′) − 7n(11 n − 29)p⁴t_(a)¹¹ t_(a)^(′2) − 7n(7n² − 58 n + 31)p³t_(a)¹⁰ t_(a)^(′3) + 7n(n³ + 67 n² − 93 n + 1)p²t_(a)⁹t_(a)^(′4) + 7 n × (9n⁴ + 36n³ − 162 n² + 4n + 17) p t_(a)⁸ t_(a)^(′5) + n(63n⁵ − 225n⁴ − 1330n³ + 230n² + 595n + 27)t_(a)⁷t_(a)^(′6) − n(27n⁵ + 595n⁴ + 230n³ − 1330n² − 225n + 63)t_(a)⁶t_(a)^(′7) − 7 n(17n⁴ + 4n³ − 162 n² + 36n + 9)p t_(a)⁵ t_(a)^(′8) − 7n(n³ − 93 n² + 67n + 1)p²t_(a)⁴ × t_(b)⁹ + 7 n(31 n² − 58n + 7)p³t_(a)³t_(a)^(′10) − 7 n(29 n − 11)p⁴t_(a)²t_(a)^(′11) + 77n p⁵t_(a)t_(a)^(′12) − 11p⁶t_(a)^(′13)].

Annex 3

An example of embodiment of the method is as follows:

** initial variables: **; h=0,3; d=20; t_(a)=−1500; t'_(a)=70; n=1,7;K_(a)=0,47; fresnel={ }; r_(c)[0]=0; r_(c)[1]=0; i=1;While[r_(c)[i]<=d/2, ** Calculation of the maximum radius of the stringfor a height h: **; {r_(c)[i] = Replace[r with FindRoot[(1−i)h+Za[n,t_(a)−(i−1) h, t'_(a)+(i−1)h, K_(a) ,r_(c)] = h, {r, 0, d/2}]]; **Definition of the next piece i + 1 up to the maximum diameter.**; ** Theobject and image distances are compensated:**; z_(a) [i+1]={−ih+z_(a)[n,t_(a)−ih, t'_(a)+ih, K_(a), r], (r >−d/2 and r = −r_(c)[i]) or ((r <d/2and r>=r_(c)[i]))}; ** Redefinition of the area of the previoussector:**; piece_z_(a)[i]={(1−i)h + z_(a) [n, t_(a) −(i−1)h,t'_(a)+(i−1) h, K_(a), r_(c)], (r > − r_(c) [i] and r = r_(c)[1− i]) or((r < r_(c)[i] and r >= r_(c) [i −1]))};  Rule = Append [ fresnel,piece_Z_(a)[i] ];  i++; ];  Rule = Append [fresnel, piece_Z_(a)[i]];Piecewise [fresnel]

The invention claimed is:
 1. A communication system comprising anoptical fiber assembly, a modulated light signal receiver and atelescope, the modulated light signal receiver being positioned at areceiving end of the optical fiber assembly, the telescope beingpositioned at a collecting end of the optical fiber assembly, themodulated light signal receiver being arranged to receive uplinkmodulated light signals collected by the telescope and travelling in theoptical fiber assembly, the telescope comprising an optical concentratorhaving an inlet face and an outlet face with a surface area smaller thanthat of the inlet face, the telescope further comprising agradient-index lens disposed with respect to the optical concentrator sothat an inlet face of the gradient-index lens extends opposite theoutlet face of the optical concentrator, the collecting end of theoptical fiber assembly opening out opposite an outlet face of thegradient-index lens.
 2. The communication system according to claim 1,wherein the inlet face of the optical concentrator has a Fresnelsurface.
 3. The communication system according to claim 2, wherein theFresnel surface comprises a plurality of areas each having a surfacedefined by a Cartesian oval.
 4. The communication system according toclaim 1, wherein the inlet face of the optical concentrator has asurface defined by a Cartesian oval.
 5. The communication systemaccording to claim 1, wherein the optical concentrator is a compoundelliptical concentrator.
 6. The communication system according to claim1, wherein a lateral surface of the concentrator has one or more lateralfacets of the prismatic type.
 7. The communication system according toclaim 1, wherein the inlet face of the gradient-index lens is bonded tothe outlet face of the optical concentrator.
 8. The communication systemaccording to claim 1, comprising a visible light transmitter positionedat an illumination end of the optical fiber assembly, the visible lighttransmitter being arranged to generate visible light that propagatesthrough the optical fiber assembly to open outwardly via the collectingend and the telescope.
 9. The communication system according to claim 1,comprising a modulated light signal transmitter positioned at atransmitting end of the optical fiber assembly, the modulated lightsignal transmitter being arranged to produce downlink modulated lightsignals which travel through the optical fiber assembly and aretransmitted externally via the collecting end and the telescope.